Late Blight Control – Date and Product Strategy Must be Correct!

Late Blight Control – Date and Product Strategy Must be Correct!

Germany, Bavaria; Bayerische Landesanstalt für Landwirtschaft

Institut für Pflanzenschutz; authors: Michael Zellner, Steffen Wagner, Bernhard Weber, Johann Hofbauer http://www.lfl.bayern.de/ips/landwirtschaft/12990/

 

This article (in English) provides very useful information and tables about the essentials in late blight control concerning the choice of product and the timing of the application. Tables of different fungicides, dates of application, a comparison of systemic and local fungicides are included. It explains the conditions for infestation, the function and modes of action of the fungicides. A selection of fungicides for first and later treatments is provided as well as optimum treatment frequency, dosage and prices.

Potato late blight control (Phytophthora infestans)

This article refers Potao late blight control in Germany achieved in 2007. A strategy is offered recommending products with different modes of action in order to prevent resistance development.

High infestation pressure occurred in 2007 and occurred mainly on leafs. The recommended strategy is to use first systemic or partial systemic treatment at the beginning of the infestation ensuring the protection of the foliage. Products based on contact activity are well suited if infestation pressure is low.

Intensive treatment (Stoppspritzung) to eliminate infections showed very good results maintaining spraying intervals and recommended dosage. The following should be observed:

-         Spraying intervals max.5 days

-         Application of full dosage of products local systemic effects combined with a spore killing product (selection):     Acrobat plus WG 2 kg/ha + Electis 1,8 kg/ha

                                                     Tanos 0,7 l/ha + Shirlan 0,3 l/ha

                                                     Valbon 1,6 l/ha + Ranman 0,2 l/ha + 0,15 FHS

                                                     Infinito 1,5 l/ha + Shirlan 0,3 l/ha

-         For the following treatment a product with good efficiency and rain persistence should be applied

-         For the continuing and final treatment (8-10 days before haulm destruction) spore killing products should be applied.

 

In order to prevent development of resistance alternating use of active ingredients is essential. An alternation of the products Valbon (no spore killing effects) and Infinito (a.I.: Fluopicolide and Propamocarb) with a different mode of action provides a good resistance strategy.

Infinito provides an antisporulant and translaminar effects providing protection to the stem and the growing leafs. Depending on infestation pressure the recommended dosage varies between 1,2 – 1,6 l in 7-10 days.

The table in the original document presents a selection of in Germany approved fungicides.

Column 1= product name; column 2 = recommended (approved) dosage; column 3= active ingredient name; column 4= active ingredient concentration; column 5= mode of action; column 6= distance to surface water (m) and reduction of drift; column 7= sensitive area requirements; column 8= price.

Prediction and manipulation of black dot development in potato crops

black-dot

The project examines factors influencing black dot development to help identifying crops at risk to reduce symptoms development through early harvesting.

One option for the management of black dot is early harvesting, which reduces symptom development. In order to select crops for early harvesting it is essential to know which crops are likely to be at risk by examining the factors influencing BD development. The research has shown that the ability to predict the risk of black dot occurring varies with potato variety. The methods of haulm destruction and the different storage conditions studied during the project did not effectively reduce the development of black dot.

Observations were made over 3-year study to try predicting black dot (BD) development on harvested tubers by assessing stems and stolons for the presence of the disease in 124 potato crops and related to the disease on the tubers at harvest. In some years significant associations were observed in some cultivars. In 2000 and 2002 in the cv. Estima if stems or stolons showed black dot symptoms as the crops were starting to senesce then the disease was likely to be present on tubers at harvest. In cv. Maris Piper a significant association between black dot on stems in September 1999 with disease at harvest was observed. No relationship between black dot on stems and stolons in the growing crop and disease on tubers at harvest were observed in the cvs. Saxon and King Edward. To explain these results a glasshouse and field experiment were performed to identify when symptoms of black dot develop on underground parts of a potato plant. These showed that infection by C. coccodes could occur soon after these plant parts had formed. Visual symptoms did not appear till just prior to senescence on stems and stolons and during senescence on tubers. Methods of haulm destruction and different storage conditions did not effectively reduce development of black dot on tubers. Reasons for this and its commercial implications are discussed.

Fight against blight: independent blight fungicide trials summary – years 2003 to 2005

report-fight-against-blight-independant-blight-fungicide-trials-2003-2005-summary

This report presents independently generated data on the effectiveness and technical attributes of blight fungicides.

The BPC commissioned ADAS & SAC to carry out field trials in 2003, 2004 & 2005, located at ADAS Rosemaund and SAC Auchincruive. Only two trials were carried out at each site in each year. The P. infestans isolates used were all recent isolates at the time from the UK. All trials were carried out on small plots of the variety King Edward. To make comparisons of all possible combinations would be prohibitively expensive therefore the work reported concentrated on two protocols:

Early season fungicides (Protocol 1): Evaluation of fungicides applied very early in the development of the crop.  Two new fungicides at the time, Sonata and Tanos, were compared with three established fungicides often used at the start of programmes, Dithane NT, Invader and Shirlan.

Main season fungicide evaluation (Protocol 2): The performance of fungicides applied from the end of rapid canopy growth was compared because most of the new fungicides are recommended for this growth phase of the crop. In addition, this would allow their effectiveness in controlling tuber blight to be evaluated. The new fungicides Electis, Ranman TP and Sonata, were compared with the established products, Curzate M, Invader and Shirlan.

The fungicides tested gave a similar level of foliar blight control. The trials provided strong data for the relative fungicide efficacies against tuber blight.

 

Project report: Independent variety trials

project-report-independent-variety-trials-2005

Varietal performance for susceptibility to blight, black dot, black scurf, silver scurf, skin spot, common scab, powdery scab, blackleg, dry rot, potato cyst nematodes and other damages

To comply with national and European Community legislation for marketing seed potatoes, varieties must be placed on the official National List (NL) of a Member State, which is then automatically entered on to the Common Catalogue (EC National List). Part of the NL testing involves assessing a new variety for Value for Cultivation or Use. In the UK, this testing is largely concentrated on assessing varietal performance for susceptibility to diseases, pests and important tuber quality characteristics.

This 28-page experimental report describes tests conducted on 4 varieties undergoing their 2nd year of UK NL testing, 7 varieties which had completed UK NL tests and 5 Common Catalogue varieties. The above varieties were tested against foliage late blight, black dot, black scurf, silver scurf and skin spot. The Common Catalogue varieties were also tested for susceptibility to common scab, powdery scab, blackleg, dry rot, potato cyst nematodes, external (splitting) and internal (bruising) damages. The report presents a comprehensive summary that covers Project Aims, Work Undertaken and Findings (results on Susceptibility/resistance for 2005 are summarised in a table and rated on 1 (Low) – 9 (High) for resistance to disease, pest and defects) and conclusions.

Fungicide Resistance Action Group UK (FRAG-UK) Potato late blight: Guidelines for managing fungicide resistance

growers-advice-potato-late-blight-guidelines-for-managing-fungicide-resistance

This guide sets out actions to minimise the risk of resistance development to existing fungicides and new active substances for control of late blight.

The introduction in the late 1970s of the phenylamides brought a new dimension to blight control but there was a rapid development of resistance in the blight pathogen. This quickly brought about a change in the number of recommended applications. Of the current approved fungicides, resistance in Phytophthora infestans has developed only to the phenylamides, which was first identified in the UK in 1981.  The report provides information on the use of fungicide, the types and occurrence of fungicide resistance and how to reduce the risk of resistance developing in a pathogen population. A list of 12 fungicide groups, their mode of action and mobility, common name of active ingredient, product name, resistance risk and use is being presented. The Impact of new strains on fungicide use is also being addressed.

Managing fungicide resistance can be summarised as follows: where possible use a blight resistant cultivar, avoid growing large areas of highly susceptible cultivars, eliminate sources of blight (infected seed, ground-keepers and dumps), monitor local weather conditions, apply fungicides as protectants, select fungicides to suit local conditions, use mixed formulations of active ingredients with different modes of action or from a different fungicide families, or target specific products in blocks to appropriate growth stages, do not chase the epidemic with fungicides, burn off early if blight levels are significant and delay lifting until the haulm has been dead for at least 14 days.

Fight against blight: Potato outgrade hygiene

growers-advice-fight-against-blight-potato-outgrade-hygiene

This report provides the best practice advice for potato outgrade control, which can act as a reservoir for blight infection.

The report focused on minimizing the impact of potato outgrades. This included easy access to outgrade piles away from potato crops and farm buildings, site piles on land not intended for any crop or any potato crop in the future, not to risk polluting watercourses, locate piles away from ditches and rivers or groundwater etc.

Control measures emphasised on adopting a zero tolerance approach to green foliage on outgrade piles by tackling it early; relying on a late application of glyphosate or diquat + paraquat is a high risk strategy as blight may already have spread by this point. The report also provides a strategy for the prevention of green foliage and highlight regulations for agricultural waste management in the UK.

Fight against Blight Issue 4: Volunteer Control (Groundkeepers)

growers-advice-fight-against-blight-volunteer-control

Growers’ advice to reduce the impact of blight through cultural methods and the use of herbicides to control volunteer potatoes.

Volunteer potatoes act as a primary infection source by over-wintering infected tubers, and provide unprotected foliage that can act as an entry point throughout the season for blight. They can also act as a reservoir or a host for other problems such as spraing, potato cyst nematodes (PCN), black scurf, black dot, powdery scab etc. Volunteers are also a host for aphids and aphid transmitted potato viruses. The report provides facts backed by evidence from trials about the problem and describes cultural and chemical methods of control as no single herbicide treatment is entirely effective.

An integrated control strategy was suggested emphasising on optimising tuber size distribution, applying maleic hydrazide, setting the harvester to lift smaller tubers where possible, keeping returned tubers near the soil surface, following with a competitive crop, hitting volunteers whenever possible, using selective herbicides in the following crops, using pre-harvest glyphosate, cleaning up stubbles with glyphosate and watching out for volunteers in shaded crops like winter oilseed rape and maize.

Fight against blight: Advice for growers of organic crops

growers-advice-fight-against-blight-advice-for-growers-of-organic-crops

Integrated measures to avoid, prevent or delay the onset of blight (Phytophthora infestans) in organically produced potatoes

The scope for fungicide use is severely limited in organic crops. This means that cultural methods of control are the foundation for blight management. This report emphasises on the integration of different cultural measures. Protectant copper compounds are currently the only fungicide used in organic potato production for blight control under high risk situations before infection takes place. However copper should still be used if blight is detected in the crop to try to slow down further spread. The report provides useful advices on the circumstances under which registered protectant chemical compounds can be used and the protocol to be followed. Protectant copper compounds were due to be prohibited in the EU from March 2002, but removal has been delayed until effective control methods are developed, though the uses of these compounds were progressively restricted.

Cultural methods that were addressed included variety choice based on NIAB (National Institute of Agricultural Botany, Cambridge) ratings, seed quality and management, site characteristics, planting date and planting, crop nutrition, irrigation, crop infection, defoliation, crop hygiene and observations. Until the end of 2005, use of copper is restricted to a maximum of 8kg of elemental copper/ha/year, then 6kg of elemental copper/ha/year thereafter, with the aim of completely phasing it out when effective alternative control methods are developed.